Neuroinflammation, a feature of neurodegenerative diseases of diverse origins, accelerates disease progression as the protective function of microglia, innate immune cells of the central nervous system is subverted by chronic stimulation into a pathological mode that endangers normal neurons. As neuron integrity becomes compromised, the environment becomes oxygen-deprived, resulting in induction of a hypoxic response which increases microvasculature in the damaged area. Components of the inflammatory and hypoxia responses are potential therapeutic targets, but these responses interact in complex and poorly understood ways. The processes of neurodegenerative disease, are not wholly autonomous features of the neuron itself, but are rather the outcome of complex interactions between the various cell types and numerous signaling pathways of these responses. These interactions are a challenge to the goal of therapeutic intervention that does not eliminate protective functions since underlying genetic networks, particularly early in the disease state, are difficult to discern. Studies of these interactions in neurodegenerative diseases have relied on cell culture systems that cannot fully emulate in vivo conditions or on complex rodent models. The basis for this R15 proposal is the discovery in a Drosophila model of Parkinson's disease of a robust neuroinflammatory response in adult brain, mediated by microglial-like hemocytes, which are insect innate immune cells. The inflammatory response occurs concurrently with an angiogenic-like growth of tracheal branches, the insect's oxygenation network, in a hypoxia response. This experimental system is a promising link between cell culture and mammalian models. The central hypothesis guiding this project is that the hypoxia and inflammatory responses are integrated through communication between hemocytes/microglia, angiogenic-like tracheal branches, and neurons. This project seeks to define the genetic networks controlling the interactions of these ancient and highly conserved responses during disease progression and to assess the validity of this model as a simple screening system for potential therapeutic compounds that target these networks. Aim 1 is to test working hypotheses regarding mechanisms of the activation of responses and the directed migration of hemocytes and trachea. Cell-specific expression of RNAi and wild type alleles of proposed components of the responses will dissect mechanisms of interactions. Aim 2 will assess the system's value as a screening system for therapeutic agents. Aim 3 proposes gene expression profiling of these responses at very early points of induction to define the underlying genetic networks that control interactions of hypoxia and inflammatory components with degenerating neurons. This project will define a novel model for advancing knowledge of complex cellular interactions that modulate neurodegenerative disease progression and provide a simple and inexpensive system for screening of therapeutics.

Public Health Relevance

This proposal concerns two responses that impact the progression of neurodegenerative disease, including Parkinson's and Alzheimer's diseases, emphasizing the relevance of this project to public health. These are the induction of a chronic inflammatory response that accelerates neuron loss and of a hypoxia response that interacts by poorly understood mechanisms. The novel system described in this proposal, based on the discovery of inflammatory and hypoxia responses during neurodegeneration in a Drosophila Parkinson's disease model offers a simple but robust system for discovering underlying genetic networks that mediate these responses.